This invention relates to the manufacture of integrated circuit, particularly power integrated circuits that employ air isolated crossovers bridging between contact sites.
Air isolated crossovers are commonly used in integrated circuit technology particularly in specialized device applications like high power transistors and amplifiers. In circuits operating below 1 GHz the skin depth of metal interconnections is larger than 2.5 xcexcm, and gold or gold alloy crossover bridges of suitable dimensions for these application are costly and difficult to manufacture with high yield.
We have developed an alternative to conventional air isolated crossovers that employs multi-chip module (MCM) technology. In this approach, less expensive metals such as aluminum can be used for interconnection. The MCM interconnections are more robust and better adapted for state of the art device packaging. In the MCM approach the transistor IC is flip chip bonded to the interconnection substrate and the air bridge is formed between the chip and the interconnection substrate. In an alternative arrangement a crossover interconnection substrate resembling an MCM chip is flip chip bonded to an integrated circuit mounted on a multi-chip or multi-component interconnection substrate. The term as xe2x80x9cair isolatedxe2x80x9d used herein is a term of art meaning that a gap exists between the crossing conductor and another conductor. The gap may be air or may be filled with insulating filler material as is well known in the art.
The term xe2x80x9ccrossoverxe2x80x9d as known in the art means an interconnection between two or more contact sites on one substrate that crosses but does not connect to one or more other contact sites, and, as described herein, exclusively interconnects the aforesaid contact sites and nothing else.